1. Field of the Invention
The present invention relates generally to the controlling of the shape and position of a deformable object. More particularly, the present invention relates to an apparatus and a method for controlling the shape and position of an object that is deformable by the application of an outside force.
2. Discussion of Related Art
The present invention is particularly useful for controlling the shape and position of an optical fiber preform. In the prior art, it is known to control the diameter of an optical fiber preform during deposition of glassy layers therein by controlling the pressure within the bore of the preform. An example of such a method is given in U.S. Pat. No. 4,280,829. In such a method, during deposition of the glassy layers, a moving hot zone is generated within the preform while reactant gases flow through the bore of the preform in order to form uniform glassy deposits within the preform. An outer diameter monitor measures the diameter of the preform and provides a signal corresponding to the measured diameter to a controller. The controller compares the signal corresponding to the measured diameter to a set point and provides a control signal to a mass flow controller. By varying the flow of gas into the bore of the preform, the pressure within the preform is maintained at the level necessary to provide the desired preform diameter.
The prior art method has several deficiencies. Often, the locally heated portion of the preform becomes distorted and deviates from the desired shape in ways other than having a diameter which does not match the set point. Such distortion may include a non-circular cross section and/or the preform is not symmetrically disposed about the axis of rotation. Such distortion makes drawing an optical fiber from the preform difficult, if not impossible. Regulating the pressure of the gases within the bore of the preform will not correct these types of distortions.